This invention relates in general to a method of producing an asphalt roofing product. More particularly, the invention relates to a method of producing an asphalt roofing product having reduced voids in the asphalt coating.
Asphalt roofing products, such as roofing shingles, roll roofing and commercial roofing, are installed on the roofs of buildings to provide protection from the elements. Typically, the roofing product is constructed of a mat such as a glass fiber mat or an organic felt, an asphalt coating material on the mat, and a surface layer of granules embedded in the asphalt coating material. During manufacture, an asphalt roofing product can experience voids in the asphalt coating. A void may comprise an enclosed pocket of air within the asphalt coating of the roofing product.
The prior art fails to address this problem. For example, U.S. Pat. No. 2,186,957 to Collings et al. discloses a method for uniformly coating a fibrous sheet with a film-forming material. Reduced pressure or vacuum is applied simultaneously with or immediately after the application of the coating film to the fibrous sheet. Such procedure results in removing air bubbles from between the newly deposited film and the fibrous sheet. U.S. Pat. No. 4,869,198 to Quillen discloses a vacuum debubbler machine used for removing entrained or surface bubbles from a liquid coating on a substrate such as a printed circuit board. The substrate is first coated and then transported to the machine for bubble removal. These patents do not suggest a method in which a coating is contacted with a vacuum prior to applying the coating. The patents are unrelated to asphalt roofing products and to the problem of asphalt coating voids. Therefore, it would be desirable to provide a method of reducing voids in an asphalt roofing product.
The above object as well as others not specifically enumerated are achieved by a method of reducing voids in an asphalt roofing product according to the invention. In the method, an asphalt coating material having air voids is contacted with a vacuum in an amount effective to reduce the voids in the coating material. A mat is coated with the coating material to make an asphalt roofing product. The vacuum contacting step occurs prior to the coating step. The vacuum contacting step causes the roofing product to have reduced voids compared to the same roofing product made with a coating material not contacted with vacuum.
In a specific embodiment of the invention, the method is applied to an asphalt roofing product made with a coating material containing from about 40% to about 80% filler.
In another specific embodiment, the method is applied in the production of asphalt roofing shingles.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.